Examples of java.util.concurrent.CountDownLatch

java.util.concurrent.CountDownLatch
void main() throws InterruptedException { CountDownLatch startSignal = new CountDownLatch(1); CountDownLatch doneSignal = new CountDownLatch(N); for (int i = 0; i < N; ++i) // create and start threads new Thread(new Worker(startSignal, doneSignal)).start(); doSomethingElse(); // don't let run yet startSignal.countDown(); // let all threads proceed doSomethingElse(); doneSignal.await(); // wait for all to finish } } class Worker implements Runnable { private final CountDownLatch startSignal; private final CountDownLatch doneSignal; Worker(CountDownLatch startSignal, CountDownLatch doneSignal) { this.startSignal = startSignal; this.doneSignal = doneSignal; } public void run() { try { startSignal.await(); doWork(); doneSignal.countDown(); } catch (InterruptedException ex) {} // return; } void doWork() { ... } }}
Another typical usage would be to divide a problem into N parts, describe each part with a Runnable that executes that portion and counts down on the latch, and queue all the Runnables to an Executor. When all sub-parts are complete, the coordinating thread will be able to pass through await. (When threads must repeatedly count down in this way, instead use a {@link CyclicBarrier}.)
```
  {@code}class Driver2  // ... void main() throws InterruptedException { CountDownLatch doneSignal = new CountDownLatch(N); Executor e = ... for (int i = 0; i < N; ++i) // create and start threads e.execute(new WorkerRunnable(doneSignal, i)); doneSignal.await();           // wait for all to finish } } class WorkerRunnable implements Runnable { private final CountDownLatch doneSignal; private final int i; WorkerRunnable(CountDownLatch doneSignal, int i) { this.doneSignal = doneSignal; this.i = i; } public void run() { try { doWork(i); doneSignal.countDown(); } catch (InterruptedException ex) {} // return; } void doWork() { ... } }}
```
Memory consistency effects: Until the count reaches zero, actions in a thread prior to calling {@code countDown()}happen-before actions following a successful return from a corresponding {@code await()} in another thread. @since 1.5 @author Doug Lea

    
    protected  void testhelper(boolean useDispatcher) throws Throwable {
        final int count=8;


        final ExecutorService executor=Executors.newFixedThreadPool(count);
        final CountDownLatch latch=new CountDownLatch(count);
        final JChannel[] channels=new JChannel[count];
        final Task[] tasks=new Task[count];


        final long start=System.currentTimeMillis();
        for(int i=0;i < count;i++) {
            if(i == 0)
                channels[i]=createChannel(true, count);
            else
                channels[i]=createChannel(channels[0]);
            
            tasks[i]=new Task(latch, channels[i],useDispatcher);
            changeMergeInterval(channels[i]);
            changeViewBundling(channels[i]);
            replaceDiscoveryProtocol(channels[i]);
        }


        for(final Task t:tasks) {
            executor.execute(t);
        }


        int timeoutToConverge=120;
        boolean successConnecting  = false;
        try {
            // Wait for all channels to finish connecting
            successConnecting=latch.await(timeoutToConverge, TimeUnit.SECONDS);            
            if(successConnecting) {
                log.info("All connected. Converging...");
                for(Task t:tasks) {
                    Throwable ex=t.getException();
                    if(ex != null)

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        Message msg=createMessage(local_addr, sender, 1L, oob, true);
        unicast.up(new Event(Event.MSG, msg));
        Util.sleep(500);




        final CountDownLatch latch=new CountDownLatch(1);
        Adder[] adders=new Adder[num_threads];
        for(int i=0; i < adders.length; i++) {
            adders[i]=new Adder(unicast, latch, counter, seqno, oob, local_addr, sender);
            adders[i].start();
        }


        long start=System.currentTimeMillis();
        latch.countDown(); // starts all adders


        lock.lock();
        try {
            while(delivered_msgs.get() < num_msgs) {
                try {

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        Message msg=createMessage(local_addr, sender, 1L, oob, true);
        unicast.up(new Event(Event.MSG, msg));
        Util.sleep(500);




        final CountDownLatch latch=new CountDownLatch(1);
        Sender[] adders=new Sender[num_threads];
        for(int i=0; i < adders.length; i++) {
            adders[i]=new Sender(unicast, latch, counter, seqno, oob, local_addr, sender);
            adders[i].start();
        }


        long start=System.currentTimeMillis();
        latch.countDown(); // starts all adders


        lock.lock();
        try {
            while(delivered_msgs.get() < num_msgs) {
                try {

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        MutableDigest digest=new MutableDigest();
        digest.add(local_addr, 0, 0, 0);
        digest.add(sender, 0, 0, 0);
        nak.down(new Event(Event.SET_DIGEST, digest));


        final CountDownLatch latch=new CountDownLatch(1);
        Sender[] adders=new Sender[num_threads];
        for(int i=0; i < adders.length; i++) {
            adders[i]=new Sender(nak, latch, counter, seqno, oob, sender);
            adders[i].start();
        }


        long start=System.currentTimeMillis();
        latch.countDown(); // starts all adders


        lock.lock();
        try {
            while(delivered_msgs.get() < num_msgs) {
                try {

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    public static void testConcurrentAdds() throws InterruptedException {
        AckReceiverWindow win=new AckReceiverWindow(1);
        final int NUM=100;
        final int NUM_THREADS=10;
        final CountDownLatch latch=new CountDownLatch(1);


        final Adder[] adders=new Adder[NUM_THREADS];
        for(int i=0; i < adders.length; i++) {
            adders[i]=new Adder(1, NUM, 10, win, latch);
        }
        for(Adder adder: adders)
            adder.start();


        latch.countDown();


        for(Adder adder: adders)
            adder.join();


        System.out.println("win = " + win);

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    @Test(invocationCount=10)
    public static void testConcurrentAddsAndRemoves() throws InterruptedException {
        AckReceiverWindow win=new AckReceiverWindow(1);
        final int NUM=100;
        final int NUM_THREADS=10;
        final CountDownLatch latch=new CountDownLatch(1);


        final Adder[] adders=new Adder[NUM_THREADS];
        for(int i=0; i < adders.length; i++) {
            adders[i]=new Adder(1, NUM, 10, win, latch);
            adders[i].start();
        }


        final AtomicInteger count=new AtomicInteger(NUM);
        final Remover[] removers=new Remover[NUM_THREADS];
        for(int i=0; i < removers.length; i++) {
            removers[i]=new Remover(win, latch, count);
            removers[i].start();
        }


        latch.countDown();


        for(Adder adder: adders)
            adder.join();


        int total=0;

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  @Test
  public void simpleConcurrentGetRequestTest() {
    int nThreads = 8;
    int nRequests = 2048;
    final CountDownLatch latch = new CountDownLatch(nRequests);
    ExecutorService executor = Executors.newFixedThreadPool(nThreads);


    for (int i = 1; i <= nRequests; i++) {
      executor.submit(new Runnable() {


        @Override
        public void run() {
          try {
            doSimpleGetRequest();
            latch.countDown();
          } catch (Exception e) {
            e.printStackTrace();
          }
        }


      });
    }
    try {
      latch.await(15 * 1000, TimeUnit.MILLISECONDS);  // max wait time
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
    if (latch.getCount() != 0) {
      assertTrue("Did not finish " + nRequests + " # of requests", false);
    }
  }

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  }


  @Test
  public void timeoutTest() throws InterruptedException {
    long now = System.currentTimeMillis();
    final CountDownLatch latch = new CountDownLatch(5);
    final AsyncCallback cb = new AsyncCallback() {


      @Override public void onCallback() { latch.countDown(); }


    };


    Timeout t1 = new Timeout(now+1000, cb);
    Timeout t2 = new Timeout(now+1200, cb);
    Timeout t3 = new Timeout(now+1400, cb);
    Timeout t4 = new Timeout(now+1600, cb);
    Timeout t5 = new Timeout(now+1800, cb);
    IOLoop.INSTANCE.addTimeout(t1);
    IOLoop.INSTANCE.addTimeout(t2);
    IOLoop.INSTANCE.addTimeout(t3);
    IOLoop.INSTANCE.addTimeout(t4);
    IOLoop.INSTANCE.addTimeout(t5);


    latch.await(5 * 1000, TimeUnit.MILLISECONDS);
    assertTrue(latch.getCount() == 0);
  }

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    assertTrue(latch.getCount() == 0);
  }
  
  @Test
  public void callbackTest() throws InterruptedException {
    final CountDownLatch latch = new CountDownLatch(5);
    final AsyncCallback cb = new AsyncCallback() {


      @Override public void onCallback() { latch.countDown(); }
    
    };
    IOLoop.INSTANCE.addCallback(cb);
    IOLoop.INSTANCE.addCallback(cb);
    IOLoop.INSTANCE.addCallback(cb);
    IOLoop.INSTANCE.addCallback(cb);
    IOLoop.INSTANCE.addCallback(cb);
    
    latch.await(5 * 1000, TimeUnit.MILLISECONDS);
    assertTrue(latch.getCount() == 0);
  }

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  //ning === http://github.com/ning/async-http-client
  @Test
  public void doSimpleAsyncRequestTestWithNing() throws IOException, InterruptedException {
    int iterations = 100;
    final CountDownLatch latch = new CountDownLatch(iterations);
    AsyncHttpClient asyncHttpClient = new AsyncHttpClient();
    for (int i = 1; i <= iterations; i++) {


      asyncHttpClient.prepareGet("http://localhost:" + PORT + "/").
      execute(new AsyncCompletionHandler<com.ning.http.client.Response>(){


        @Override
        public com.ning.http.client.Response onCompleted(com.ning.http.client.Response response) throws Exception{
          String body = response.getResponseBody();
          assertEquals(expectedPayload, body);
          {
            List<String> expectedHeaders = Arrays.asList(new String[] {"Server", "Date", "Content-Length", "Etag", "Connection"});
            assertEquals(200, response.getStatusCode());
            assertEquals(expectedHeaders.size(), response.getHeaders().size());
            for (String header : expectedHeaders) {
              assertTrue(response.getHeader(header) != null);
            }
            assertEquals(expectedPayload.length()+"", response.getHeader("Content-Length"));
          }
          latch.countDown();
          return response;
        }


        @Override
        public void onThrowable(Throwable t){
          assertTrue(false);
        }


      });
    }
    latch.await(15 * 1000, TimeUnit.MILLISECONDS);
    assertEquals(0, latch.getCount());
  }

View Full Code Here

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